This is a metonym for David directing the priests, who performed the actual sacrifices. (See: [[rc://en/ta/man/translate/figs-metonymy]])
# he blessed the people in the name of Yahweh
To bless "in the name of Yahweh" means to bless with Yahweh's power and authority or as his representative. (See: [[rc://en/ta/man/translate/figs-metonymy]])